This invention relates to a spool valve and more particularly relates to a spool valve which is suitable for a hydraulic brake device for a vehicle.
With respect to a hydraulic brake device for a vehicle, a variety of devices are known. For example, Japanese Patent Application Laid-Open Publication No. 11-34852 discloses a hydraulic brake device having a regulator which regulates the braking pressure by a spool valve. The hydraulic brake device described in this publication includes an auxiliary hydraulic pressure source for increasing the pressure of the brake fluid to a predetermined pressure and for outputting a power hydraulic pressure, a control piston fluidtightly and slidably accommodated in a cylinder body ahead of a master piston and disposed so as to work with the master piston and a regulator for introducing the power hydraulic pressure outputted from the auxiliary hydraulic pressure source, for driving the spool valve in response to the movement of the control piston and for regulating to a predetermined pressure and the master piston assisted by the outputted hydraulic pressure of the regulator which is applied to a power chamber of a master cylinder.
The spool valve used for the regulator in the above publication generally includes a sleeve (a cylinder) and a spool, and is constituted so that the pressure of the fluid (for example, brake fluid) is regulated by the introduction and/or the discharge of the fluid into the sleeve in response to the movement of the spool. In concrete terms, a cylinder bore, a first communicating hole which is opened into the cylinder bore and a second communicating hole which is opened into the cylinder bore and which is separated from the first communicating hole with a predetermined distance in the axial direction of the cylinder bore are formed on the sleeve and the spool is fluidtightly accommodated in the cylinder bore so as to able to slide and is provided with an one end portion which opens and closes the first communicating hole in response to the sliding operation thereof and the other end portion which opens and closes the second communicating hole is response to the sliding operation thereof.
In order to smooth the introduction of the fluid into the cylinder bore of the sleeve, especially, in order to decrease a flow velocity noise or a hitting sound generated at the introduction of the high pressurized fluid and to prevent the cavitation from generating, in general, an inclined surface which decreases progressively a diameter of the spool outwardly is formed on both ends of the spool. In this case, since the measure of an intermediate portion of the spool extending to the positions where the inclined surfaces start becomes the criterion for determining the open and close of the first and second communicating holes of the sleeve, the strict dimensional accuracy is required for setting the relative location between the spool and the sleeve adequately. Accordingly, it is necessary to process the inclined surface of the both end portions of the spool with a high degree of accuracy. However, for example, since the measure of the intermediate portion of the spool changes when the outer circumferential surface of the spool is grinded, it is murderous to set the measure of the intermediate portion of the spool to a predetermined value. Thereby, it is difficult to produce in large quantities and the cost is increased.
An object of the present invention is to provide a spool valve which can set the relative location between the spool and the sleeve adequately and easily with simple structures and which can ensure the smooth flow of the fluid.
A spool valve includes a sleeve having a cylinder bore, a first communicating hole which is opened into the cylinder bore and a second communicating hole which is opened into the cylinder bore and which is separated from the first communicating hole with a predetermined distance in the axial direction of the cylinder bore, and a spool fluidtightly accommodated in the cylinder bore so as to able to slide and having an one end portion which opens and closes the first communicating hole in response to the sliding operation thereof and the other end portion which opens and closes the second communicating hole is response to the sliding operation thereof. A step portion having an end surface which is approximately at right angle to the axis of the spool from an outer circumference and an inclined surface which decreases progressively a diameter of the spool from the end surface toward the outside of the spool is formed on at least one of the one end portion and the other end portion of the spool. The communicating condition at an intermediate position between a closed position and a full opened position is included in the above open of the first and second communicating holes.
It is desirable that the inclined surface is constituted by a plurality of inclined surfaces. Also, a boundary between the end surface and the inclined surface may be formed by a consecutive curved surface. Further, it is desirable that the spool has a groove which is formed on the outer circumference and that the inclined surface is consecutively formed until the groove.